(101b) Acid Catalysis over Low-Silica Faujasite Zeolites | AIChE

(101b) Acid Catalysis over Low-Silica Faujasite Zeolites


Li, X. - Presenter, University of Minnesota
Han, H., Dalian University of Technology
Xu, W., Argonne National Laboratory
Hwang, S. J., Caltech
Shi, Z., University of Minnesota
Lu, P., Johns Hopkins University
Tsapatsis, M., Johns Hopkins University
Bhan, A., University of Minnesota
Low-silica faujasite (FAU) zeolites (with Si/Al ratio of ca. 1.2~1.8) sustain framework integrity and porosity upon moderate ion exchange (0.01 M of NH4NO3 solution for 1 hour at ambient temperature), which introduces two kinds of protons, distinctive in reactivity and coordination to the zeolite framework, within supercages (HSUP). Moderate ion exchange limited within supercages transpires while maintaining full occupancy of Na+ cations within associated sodalite cages; this in turn helps stabilize the framework of low-silica H-FAU zeolites. Protons located on site II (H3630) and site III (H3650) within supercages on low-silica FAU zeolites can be classified and enumerated by virtue of infrared spectroscopy, providing an opportunity to compare reactivities of these distinct protons for monomolecular protolytic reactions of propane. Protons on site II exhibit prominently higher reactivity for monomolecular propane dehydrogenation and cracking than protons on site III. Low-silica proton-form FAU zeolites (zeolite X) upon moderate ion exchange possess protons on site III that are unavailable on high-silica FAU zeolites (zeolite Y) and limit ion exchange within supercages, providing unprecedented high-temperature structural and chemical stability (>773 K) and enabling their application as solid acid catalysts.